Highly re-configurable RF receivers and challenges … re-configurable RF receivers and challenges towards a true ... to up-conversion mixer of Aux. path. LO Auxiliary Path RX down

Highly reHighly re--configurable RF receivers and configurable RF receivers and challenges towards a true SDR receiverchallenges towards a true SDR receiver

Naveen YanduruTexas Instruments Inc.

1

Outline

• The need for highly reconfigurable “multi-band, multi-mode”SDR receiver.

• Multi-band receiver: Design directions and challenges.

• Multi-mode receiver: Architecture and design strategy for a re-configurable receiver.

• A WCDMA, GSM/EDGE “multi-mode” RF receiver front-end in 90nm CMOS.

• Conclusion.

2

Plethora of wireless applications for the mobile terminal

GPS

Voice, Data:

GSM/EDGE WCDMA WLAN WiMAX

DVB-H

Bluetooth

3

Multiple bands across the frequency spectrum

Multiple receiver bands,

Mobile standards

MIMO/Diversity

Co-existence

GSM E GSM PCS IMT2K ISM

0.8G 0.9G 1.6G 1.8G 1.9G 2.1G 2.4G 3.5G 5.2G2.6G0.6G

DCS

WCDMA

WLAN (802.11a/b/g)

WiMAX

DVB-H

GSM/EDGE

Bluetooth

GPS

Need for efficient receiver hardware re-use

5.8G

4

Need for receiver hardware re-configurability

Multiple Bands

Multiple Standards

Duplex Schemes(FDD/HFDD/TDD)

Modulation (Amplitude with PAR,

Phase only)

Signal Bandwidths(narrow band, spread spectrum)

Highly Re-Configurable “Multi-Mode” Receiver

True Software Defined Radio Receiver

(Multi-Band, Multi-Mode)

Need an agile “multi-band, multi-mode”receiver with programmable performance

combinations

6

Outline





• Conclusion.

7

Pre-Select Filter Bottleneck

Dedicated RX input pins, Matching Networks, LNA input stages are required.

Pre-Select Filters (Duplexer/SAW/BAW) are band specific.

1.9G LNAMatch

RF IC1.8G LNA

Match

2.6G LNAMatch

2.1G LNAMatch

0.9G LNAMatch

0.8G LNAMatch

LC

TANK

LC

TANK

LC

TANK

Can we overcome this bottleneck?

9

High dynamic range RF ADC

• Nyquist rate as high as 10GHz.• Dynamic range requirement of 100dB or more.

• Complete spectrum is converted to digital.• A very powerful receiver!

• State of the art ADCs are not able to meet this required performance.

10

Integrated Tunable RF Bandpass Filters

Dynamic range issues based on low Q of on-chip inductors. Issues with channel based tuning and tuning range.Input gm linearity is still an issue.

gmi gmo

K

CouplingTo

Mixer

[Ref] Kuhn, W.B.; Yanduru, N.K.; Wyszynski, A.S., “Q-enhanced LC bandpass filters for integrated wireless applications”, IEEE-MTT Dec. 1998.

11

RF filtering using MEMS• MEMS based RF filters using switchable capacitors for tuning have been shown.

• Low loss switches using MEMS can be used to switch between various RF filters.

MEMSSwitch

Broad-band LNA

• Issues such as reliability, yield and complexities in integrating mechanical structures with transistors need to be considered.

RF MEMS tunable filters

[Ref] Nguyen C. T –C, “RF MEMS in wireless Architectures”, DAC 2005.

[Ref] S.-J Park, K.-Y Lee, G.M. Rebeiz, “Low-Loss 5.15 to 5.70-GHz RF MEMS Switchable Filter for Wireless LAN Applications”IEEE-MTT, Nov. 2006.

12

Clock driven discrete time filtering after RF down conversion

Input linearity of the LNA and Mixer in the absence of any RF filtering needs to be addressed.

Clock driven discrete time analog filtering

with anti-alias notches followed by ADC

Wideband LNA

I

QClock driven discrete time

analog filtering with anti-alias notches

followed by ADC

[Ref] Abidi, A. A., “Evolution of a Software-Defined Radio Receiver’s RF Front End,” IEEE RFIC Symposium 2006.

[Ref] Muhammad, K., et al, “The First Fully Integrated Quad-Band GSM/GPRS Receiver in a 90-nm Digital CMOS Process”IEEE JSSC, Aug. 2006.

13

Discrete time analog filtering (cont.)

• Advantages– Digital process friendly base-band filtering.– Easy programmability of base-band filtering between modes and for

notches.

• Disadvantages– Main issue of linearity of LNA, mixer needs to be addressed.

Switched Capacitor filter

IIR1

CR1 CB1

IIR2

CR1 CB1

MIX

14

Feed forward cancellation of blockers

• Advantages– Removes in-band and out-of-band blockers.– Relaxes linearity for the Mixer.

• Disadvantages– Mismatch issues with gain and phase inversion between the main and aux. path.– LNA linearity still a challenge, – Phase noise requirement is shifted to up-conversion mixer of Aux. path.

LO

Auxiliary Path

RX down conversion

HPF

[Ref] R. Gharpurey, S. Ayazian, “Feedforward Interference Cancellation in Narrow-Band Receivers” 2006 IEEE Dallas/CAS Workshop, Oct. 2006.

[Ref] H. Darabi, “A Blocker Filtering Technique for Wireless Receivers”, ISSCC 2007.

Some other approaches including blocker detection using fast RSSI and subsequent reduction in RF gain have been investigated.

But these schemes along with other schemes discussed are not able to match the RF performance of a receiver with pre-select filter.

16

Outline





• Conclusion.

17

Direct Conversion as Receiver Architecture

Advantages:Reduced hardware (Image rejection/filtering, Signal processing, Synthesizer)

Issues:Second order inter-modulation/“self-mixing” issues with modulated blockers. Flicker noise.LO leakage and dc offsets.

A “Near-Zero or Low-IF” architecture can be used if image rejection requirements are not too difficult.

18

2nd order inter-modulation distortion in direct conversion receiver

LNADuplexer

PA

PLL

90o

TX Leakage

TX self mixing distortion

FTX FRX FRXFTX

FBB

LNADuplexer

PA

PLL

90o

TX Leakage


FTX FRX FRXFTX

FBB

Figure showing IM2 distortion from modulated TX blocker in FDD mode.

Any modulated blocker with non-constant envelope (AM) causes this distortion.

19

Distortion in the presence of LO leakage in Direct Conversion Receivers (1)

ω1-ω2 , ω2-ω1 at the output of the mixer looks like an IM2 component. (Can misleadingly imply an IP2 issue!)

But really it is the LO leakage and IP3 that is the problem!

LO

ω1ω2ωLOω1ω2ωLOω ω ω0

ωLO+ω2-ω1ωLO+ω1-ω2

ω2-ω1ω1-ω2

Direct Down Converter

LNA with finite IP3

LO Leakage

LPF

Wanted Signal

20

Distortion in the presence of LO leakage in Direct Conversion Receivers (2)

Distortion caused by an AM blocker will have similar issue like the two tone case shown earlier.

LO

ωbωLO ωbωLOω ω ω0

Direct Down Converter

LNA with finite IP3

LO Leakage

LPF

Distortion

21

Performance re-configurability in RF front end

A high dynamic range RF Front End design is the starting point.

Need to be able to program this front end for various combinations of noise/linearity/power.

Need to have little degradation in overall performance between various programming modes.

High Linearity mode – FDD mode, higher input signal conditions.

Low Noise mode – TDD mode, sensitivity conditions.

Low Power mode – high input signal, low level of blockers.

Linearity/(Noise*Power) ~ Constant

22

Outline





• Conclusion.

23

A WCDMA, GSM/GPRS/EDGE “multi-mode” RF Receiver Front

End in 90nm CMOS

24

Linearity bottleneck in WCDMA receiver- IIP2 based on TX leakage

LNADuplexer

PA

PLL

90o

TX Leakage


FTX FRX FRXFTX

FBB

LNADuplexer

PA

PLL

90o

TX Leakage


FTX FRX FRXFTX

FBB

Input IP2 = 2PTX – PIM2 – “Adj_N”

Where,

PIM2 is the input referred IM product;

“Adj_N” is the adjustment factor which depends on no. of channels in the TX leakage

[Ref] Khan, M.S.; Yanduru, N., “Analysis and Measurement of Self Mixing of Transmitter Leakage in WCDMA Receivers,”IEEE-RWS 2007.

25

Linearity bottleneck in WCDMA receiver- IIP3 from TX leakage, blocker

LNADuplexer

PA

PLL

90o

TX Leakage

IM3 distortionFTX

FBB

FBLK FRXLNADuplexer

PA

PLL

90o

TX Leakage

IM3 distortionFTX

FBB

FBLK FRX

Input IP3 = (2PBLK+PTX–PIM3+ “Adj_N”) / 2

Where,

PIM3 is the input referred IM product;

“Adj_N” is the adjustment factor which depends on no. of channels in the AM blocker.

[Ref] Khan, M.S.; Yanduru, N., “Analysis of Signal Distortion due to Third Order Non-Linearity in WCDMA Receivers,” IEEE ISCAS 2006.

26

Spectral re-growth of WCDMA adjacent channel

Input IP3 = (3PADJ–PIM+ “Adj_N”) / 2

Where,

PIM is the input referred Spectral re-growth product;

“Adj_N” is the adjustment factor which depends on no. of channels in the AM blocker.

Khan, M.S.; Yanduru, N., “Signal Distortion Due To Spectral Re-Growth of Adjacent Channel Interferers in WCDMA Receivers,”IEEE-RWS 2007.

27

Key RF Performance Specifications

RF Parameter GGE Mode (GSM/GPRS/EDGE)

WCDMA Mode

Units

NF 2.5 3.0 dB

IIP3 -18 -7 dBm

IIP2 40 44 dBm

Signal Bandwidth 0.2 3.84 MHz

• Higher LNA gain in GSM mode

• Adjust base band filter corner based on signal bandwidth

• Trade IP3 with current in GSM mode.

28

Receiver Block Diagram

Digital

DC Estimation

ADC

LNA LCLOAD

Dividers

DC Correction

ADC

PLL

900RF IN

To DBB

To DBB

Current Chip Presented

Digital

Digital

DC Estimation

ADC

LNALNA LCLOAD

Dividers

DC Correction

ADCADC

PLL

900RF IN

To DBB

To DBB

Current Chip Presented

Digital

RF Front End designed in 90nm CMOS

No inter-stage SAW between LNA and Mixer!

[Ref] Yanduru, N. K, et al, “A WCDMA, GSM/GPRS/EDGE Receiver Front End without Interstage SAW Filter,” IEEE RFIC Symposium 2006,

29

Pros & Cons

• Pros+ Design in 90nm CMOS+ Highly integrated receiver

• Cons – Uses 2.4V supply for the mixer (rest of the chip uses

1.4V)– Use of bond-wire inductor for the tuned LC LNA load

30

LNA R L

VOUT+

Mcasc1

VRF

RB1

M1

Vbias

Vbias_casc

Vdd

C L

VOUT-

M2

Mcasc2

LL1 LL2

RB2

C C

Gain Control

Current/Linearity/Gain Control

31

RF Amp and Mixer Current, Linearity, Gain Control

Signal BW Control

32

GND

VDDA VGA

Gain, Linearity , Current Controls

Signal BW Control

33

WCDMA measured performance - Band III

Parameter Measured performance

37.3 dB

2.90 dB

-10.8 dBm

-7.3 dBm

-3.75 dBm

47.0 dBm

Voltage gain

NF

In band IIP3

Out of band IIP3(CW blockers at TX and TX+47.5MHz)

Out of band IIP3(CW blockers at TX and TX-95MHz)

Out of band IIP2(2 CW blockers at TX freq.)

34

GGE measured performance – DCS band


37.3 dB

2.90 dB

NF under blocking (3MHz blocker at -23dBm), includes reciprocal mixing 8.64dB

-10.8 dBm

44.0 dBm

Voltage gain

NF

IIP3(blockers at 800kHz and 1600kHz offset)

IIP2(self-mixing of blockers at 6MHz offset)

35

More Measured performance


-14 dB

50 uV

Gain imbalance (WCDMA) 0.4 dB

Phase imbalance (WCDMA) 4o

Phase Imbalance (GGE) 1o

Out of Band IIP2 (WCDMA)(CW blockers at RX+TX and TX)

34.7 dBm

0.3 dB

S11

Output DC offset (after correction)

Gain Imbalance (GGE)

36

VGA voltage gain curve

Voltage Gain vs VGA Gain Setting

0

10

20

30

40

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12VGA Gain Setting [dB]

RX

Volta

ge G

ain

[dB

]

LNA High Gain Mode

LNA Mid Gain Mode

37

NF vs. VGA Gain Setting

NF vs VGA Gain Setting

0

2

4

6

8

10

12

-14 -10 -6 -2 2 6 10

VGA Gain Setting [dB]

NF

[dB

]

LNA High Gain - NF

LNA Mid Gain - NF

38

Measured spectral re-growth based on number of channels in adjacent channel

Re-growth of a 16 DPCH WCDMA ACIRe-growth of a 1 DPCH WCDMA ACI

High PAR/increase in channels in adjacent channel will cause increased spectral re-growth.

39

Die Photo

40

High Dynamic range ADCs

ADC

LO

RF

Filtering to reduce the power of blockers before the ADC. Also serves as anti-alias

Gain to reduce the impact of ADC noise on RX sensitivity.

Also some gain control.

High dynamic range; (Over sampled with noise shaping)

Channel select filtering and signal AGC can be moved into Digital.

• High dynamic range in the ADC reduces the filtering and gain required in the analog (lower analog signal processing).

41

3rd Order continuous time ΣΔ ADC

4bit

IN OUT<3:0>

GGE GGE GGE

GGE GGE GGE

Loop delay compensation

WCDMA

gm1 gm2 gm3

gf1

SH

gf2

g

g

• Digital programmability for STF, NTF control.

• Gms, capacitors, clock rate, reference level, feedback currents are digitally programmable.

42

ADC simulated performanceSimulation results in

WCDMA modeSimulation results in

GGE mode

1.92 0.2

Sampling Frequency 120MHz 56MHz MHz

Quantizer levels 9 9 MHz

Peak Signal 75 150 mVpk

Noise 5.83 8.0 nVrms/sqrt(Hz)

89.5

2.1(0.8MHz, 0.16MHz blockers)

1.4V

9.0

76.2

-0.5(3.5MHz, 5.9MHz blockers)

1.4V

Current consumption (I&Q)

8.0 mA

Units

MHz

dB

dBVrms

V

IIP3

Signal Bandwidth

Dynamic Range

Supply

43

LO Generation• Key Considerations

– Tuning Range for desired band coverage (consider switchableinductor)

– Phase noise requirement based on reciprocal mixing.

– Dividers for quadraturegeneration and low-band coverage.

VbiasCK

CKB

CKB

LOPQ

LONQ

LOPI

LONI

CK

Quadrature DividerVCO

44

Outline





• Conclusion.

45

Conclusion

The need for SDR style “multi-band, multi-mode” receivers is highlighted.

Multi-band receiver: Various approaches and directions in trying to achieve this goal are presented.

Multi-mode receiver: A multi-mode receiver in 90nm CMOS is presented illustrating the multi-mode concepts.

Once a clear winner showing the performance and requirements for multi-band receiver emerges, we will have the much needed SDR receiver.

46

Acknowledgements

• Fikret Dulger• Danielle Griffith• Irene Deng• Kah-Mun Low• CC Chen• Shanthi Bhagavatheeswaran

47

References

• Kuhn, W.B.; Yanduru, N.K.; Wyszynski, A.S., “Q-enhanced LC bandpass filters for integrated wireless applications”, Microwave Theory and Techniques, IEEE Transactions on, Vol. 46, Issue: 12 , Dec. 1998.

• W.B. Kuhn, “Fully integrated bandpass filters for wireless transceivers-problems and promises” MWSCAS-2002, Volume 2, 4-7 Aug. 2002 Page(s):II-69 - II-72 vol.2

• Nguyen C. T –C, “RF MEMS in wireless Architectures”, DAC 2005, June 13 -17 2005, Page(s): 416 – 420.• S.-J Park, K.-Y Lee, G.M. Rebeiz, “Low-Loss 5.15 to 5.70-GHz RF MEMS Switchable Filter for Wireless LAN Applications”

IEEE Transactions on Microwave Theory and Techniques, Vol 54, Issue 11, Nov. 2006 Page(s):3931 – 3939.• Muhammad, K., et al, “The First Fully Integrated Quad-Band GSM/GPRS Receiver in a 90-nm Digital CMOS Process” Solid-

State Circuits, IEEE Journal of, Vol. 41, Issue 8, Aug. 2006 Page(s):1772 – 1783.• Abidi, A. A., “Evolution of a Software-Defined Radio Receiver’s RF Front End,” RFIC Symposium 2006, Page(s):27 – 30.• R. Gharpurey, S. Ayazian, “Feedforward Interference Cancellation in Narrow-Band Receivers” 2006 IEEE Dallas/CAS

Workshop, Oct. 2006 Page(s):67 – 70.• H. Darabi, “A Blocker Filtering Technique for Wireless Receivers”, ISSCC 2007, Page(s):84 - 85 Vol. 1• Khan, M.S.; Yanduru, N., “Analysis and Measurement of Self Mixing of Transmitter Leakage in WCDMA Receivers,”

RAWCON 2007.• Khan, M.S.; Yanduru, N., “Analysis of Signal Distortion due to Third Order Non-Linearity in WCDMA Receivers,” IEEE

ISCAS 2006.• Khan, M.S.; Yanduru, N., “Signal Distortion Due To Spectral Re-Growth of Adjacent Channel Interferers in WCDMA

Receivers,” RAWCON 2007.• Yanduru, N. K, et al, “A WCDMA, GSM/GPRS/EDGE Receiver Front End without Interstage SAW Filter,” RFIC Symposium

2006, Page(s):19 – 22.• P. Fontaine, A.N. Mohieldin, A. Bellaouar, “A low-noise low-voltage CT Delta Sigma modulator with digital compensation of

excess loop delay” ISSCC 2005, 6-10 Feb. 2005 Page(s):498 - 613 Vol. 1• Ali Ahmad W. Y., “Effective IM2 estimation for two-tone and WCDMA modulated blockers in zero-IF receivers”, RF Design,

April 2004.• Khan, M.S.; Yanduru, N., “Analysis of self mixing of transmitter interference in WCDMA receivers,” ISCAS 2006.

Proceedings. 2006 IEEE International Symposium on; 21-24 May 2006 Page(s):4 pp.• Manstretta, D.; Brandolini, M.; Svelto, F., “Second-order intermodulation mechanisms in CMOS down converters”, Solid-

State Circuits, IEEE Journal of, Volume 38, Issue 3, March 2003 Page(s):394 – 406.• Elahi, I.; Muhammad, K.; Balsara, P.T., “IIP2 and DC Offsets in the Presence of Leakage at LO Frequency”, IEEE

Transactions on Circuits and Systems II: Express Briefs, Volume 53, Issue 8, Aug. 2006 Page(s):647 – 651.• Craninckx, J, et al, “A Fully Reconfigurable Software-Defined Radio Transceiver in 0.13μm CMOS,” IEEE ISSCC 2007

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Highly re-configurable RF receivers and challenges … re-configurable RF receivers and challenges towards a true ... to up-conversion mixer of Aux. path. LO Auxiliary Path RX down